Generally, sheet feeding devices capable of high speed feeding are relatively complicated, and require a large number of complex and interrelated moving parts which are subject to wearing out and failure.
Most known sheet feeders cannot dispense sheets in a shingled manner, but rather, only one sheet at a time. The ability to shingle sheets would greatly increase the efficiency of any feeder device, however, most feeder devices lack this ability. Also, most friction feed devices have problems feeding coated and slick stacks.
Prior sheet feeder devices use suction cups to engage the bottom of the sheet being fed. The suction cups then pull the sheet downward and a separator member holds the sheet downward by inserting itself between the stack of sheets and the suctioned sheet. Then, a gripper arm member pulls the suctioned piece out and drops the sheet onto a conveyor belt for individual processing. The use of the suction cup presents numerous problems for different applications. For example, if the sheet being fed is a folded sheet of paper, the suction cup can adhere only to the lower portion of the folded paper. Consequently, the separator member does not separate between two separate sheets in the stack but rather between different folds of the same sheet.
Another problem with the suction cup method is that it is unable to adequately perform when the sheets are made of a stiff material rather than a flexible material since the suction is not strong enough to bend the sheet.
Yet another problem with prior sheet feeder devices is the wearing out of parts of the device. In devices with a stationary top roller, this top roller often wore out and was expensive and inconvenient to replace.
Still another problem with earlier sheet feeders is the separation of sheets having a static electrical charge. These sheets tend to resist separation resulting in multiple sheets per package.
An additional problem with prior devices includes the inability to use tall stacks of sheets because of the resulting increase in pressure upon sheets at the bottom of the stack.